Hotel heiress Paris Hilton's mobile phone account and those of other T-Mobile customers may have fallen victim to hackers who took advantage of a gaping hole in the company's Web site to steal information, according to security experts and those familiar with the incident.

A flaw in a Web site feature to reset T-Mobile account passwords is believed have played a role in hacking Hilton's T-Mobile Sidekick account, which resulted in her star-studded address book, photos, e-mail messages, and voice mail being posted for public consumption on the Internet. The password reset hole is just one of hundreds, or even thousands, of similar flaws in the mobile provider's Web page that could provide easy access to malicious hackers, according to an analysis by one security expert.

A spokesperson for T-Mobile USA declined to comment specifically on the password reset exploit or on the security of the company's Web site despite repeated requests. In an e-mail statement attributed to Sue Swenson, Chief Operating Officer of T-Mobile USA, the company says that it cares about protecting the security and privacy of its customers, and that the company is "aggressively investigating the illegal dissemination of information over the Internet of T-Mobile customers' personal data."

Rumors about what was responsible for the hack on Hilton's Sidekick have been in abundance since her account was posted for public review on Web sites around the world on February 20. Leading theories on the hack's source suggest that it may have been linked to a 2003 hack by Nicolas Jacobsen, the 22-year-old who pleaded guilty on February 15 to compromising the accounts of 400 T-Mobile customers, or the result of an easy-to-guess password on Hilton's account.

Company's Web Site to Blame?

But the hack on Hilton's account and those of other T-Mobile account holders may in fact be fallout from a technical analysis of the company's Web site based on information in an affidavit filed in the Jacobsen case by U.S. Secret Service agent Matthew Ferrante.

In a February 17 blog posting, Jack Koziol, a senior instructor at InfoSec Institute, used information in the affidavit and publicly available information on T-Mobile's site to discuss the strategy that Jacobsen used to compromise T-Mobile's servers in 2003, including a hack of Hilton's account.

Koziol speculated that Jacobsen used a SQL (Structured Query Language) injection attack to compromise T-Mobile's servers and noted that, as of his posting, there were "literally hundreds of injection vulnerabilities littered throughout the T-Mobile website," according to his blog, "Ethical Hacking and Computer Forensics."

In a SQL injection attack, attackers use a SQL database query to send, or "inject," unexpected commands into a SQL database, allowing them to manipulate the database's contents.

In the early morning of February 19, Koziol received an e-mail from a reader complimenting him on his blog. The e-mail contained an exploit for a T-Mobile Web site hole that allowed anyone to gain access to a T-Mobile account from the T-mobile.com Web site, as long as they knew the account holder's T-Mobile phone number. In the e-mail message, the exploit was attributed to a hacking group called "DFNCTSC Team."

"I know you said you cant exploit stuff, cause you are all white hat and work in the industry, but i am not legal age yet to go to jail, so i can," the message reads, in part.

Hilton's address book first appeared on the Internet on February 20. Posts of the information were accompanied by a message that claimed credit for the hack for DFNCTSC.

The exploit described in the e-mail to Koziol takes advantage of a flaw in a password reset feature in T-Mobile's Web site. Visitors who have a valid T-Mobile phone number can use the feature to receive a unique token to reset their passwords. A flaw in the design of the reset feature allows Internet users who know the URL of the password reset page to bypass a user authentication page and change an account's password without having to provide information that proves they are the account's owner, according to Koziol.

"It's a session management problem. [T-Mobile] fails to properly keep track of where users are," Koziol says. "It's not an earth-shattering vulnerability that takes a PhD in computer science to figure out. It's something a couple curious kids could do."

Koziol strongly encourages the e-mail's author, who uses the online name "luckstr4w," not to attempt to hack T-Mobile's site, citing Nicholas Jacobsen's case as an example of serious consequences that could result.

Claiming Responsibility

Contacted by e-mail by IDG News Service, luckstr4w took credit for discovering the vulnerability and writing the exploit after reading Koziol's blog. Luckstr4w denied responsibility for the Hilton hack, saying an acquaintance, who knew Hilton's phone number, used it to change her account password and access her account.

However, in the same e-mail message, luckstr4w also claimed to have changed Hilton's account password to his handle, "luckstr4w," when he and his acquaintances took control of her account.

Luckstr4w insisted on communicating solely through an anonymous e-mail account, citing fears that phone conversations or other kinds of communications would be monitored.

However, the exploit luckstr4w takes credit for writing appears to have been around for much longer. An identical version of it is included in a ZIP file called "tMobile exploit tools" was posted in October on the illmob.org Web site, in a section reserved for "zero day," or previously unknown exploits, according to an Illmob member who uses the online name "Pingywon."

Illmob.org was one of the first Web sites to display the Hilton address book information, though the group denies any involvement in the hack or any knowledge of how the address book was stolen, says Pingywon, who described himself as a news poster for Illmob.org, but not the person who posted the Hilton address book.

Sources within the hacking community said that both luckstr4w and the DFNCTSC are unknown. However, whether or not luckstr4w was the author of the password reset exploit, the hole it took advantage of--if left unpatched by T-Mobile--was big enough that even inexperienced hackers, or "script kiddies," could use it, provided they knew where to look, experts agree.

Phone Phreaking

Hilton's phone number, which is needed to carry out the hack, was also circulated widely within phone hacking (or "phone phreaking") circles prior to the hack, according to lucky225, a self-described phone phreaker, or hacker, who declined to use his real name.

Phone phreakers took advantage of loose security on T-Mobile's voice mail system and a flaw in Caller ID technology to peruse Hilton's voice mailbox and that of her sister, Nicky, and other celebrities. The Hilton sisters' T-Mobile phone numbers were widely shared on multiuser party lines that are popular meeting places in the phone phreaking community, he says.

The ready availability of Hilton's number and of an exploit that could be used, with it, to give Internet users access to her T-Mobile accounts means that the potential list of suspects for the hack is very long.

However, if luckstr4w's account of the T-Mobile hack is true, it casts doubt on other leading theories of how Hilton's Sidekick was compromised. Observers have theorized that her address book was taken by Jacobsen more than a year ago and only recently surfaced, or that the heiress had an easy-to-guess password.

Regardless of who is responsible for the hack, the bigger problem is with T-Mobile and its public-facing Web sites, experts agree.

The company's Web site is a tangle of hundreds or thousands of large and small security holes that would appear on even a routine scan of the company's Web site using any vulnerability scanning tool, Koziol says.

He expressed shock that the company had apparently fixed the hole Jacobsen used in 2003, without doing a larger security review of their site that would have turned up other problems.

Koziol says the problems facing T-Mobile's Web site are common to companies that move quickly to open their corporate networks to the Internet through Web based applications, but adds that T-Mobile's case is extreme.

"They haven't done Web Security 101. I see many mistakes that they make over and over again. They're mostly injection vulnerabilities--people being able to insert [malicious] code where they shouldn't," he says.

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